Reefing line cutter

ABSTRACT

AN EXPOSIVELY ACTUATED CUTTER ASSEMBLY FOR SEVERING THE REEFING LINES WHICH HOLD TOGETHER THE CANOPY OF A PARACHUTE AS THE LATTER IS DEPLOYED. THE EXPLOSIVE WHICH DRIVES THE CUTTER BLADE THROUGH THE REEFING LINE IS DETONATED BY UTILIZING THE TENSION DEVELOPED IN THE REEFING LINE BY THE TENDENCY OF THE PARACHUTE TO UNFURL TO DRIVE A FIRING PIN AGAINST A PRIMER. THE EXPLOSIVE TRAIN WITHIN EACH CUTTER ASSEMBLY MAY BE IDENTICAL, THAT IS, THERE IS NO NECESSITY FOR DIFFERENT DELAY TIMES TO PROVIDE SEQUENTIAL SEVERING OF THE REEFING LINES TO THAT NEAREST THE PARACHUTE CANOPY APEX FROM THE LOAD SINCE THE REEFING LINES ARE AUTOMATICALLY TENSIONED IN THAT ORDER AS THE PARACHUTE IS UNFURLED. AN INEXPENSIVE BRACKET IS PROVIDED IN COMBINATION WITH THE MOVABLE CUTTER ASSEMBLY TO HOLD THE REEFING LINE WITH AN   INITIAL KINK OR BEND WHICH IS STRAIGHTENED BY TENSION IN THE LINE, THEREBY CAUSING RELATIVE MOVEMENT OF THE BRACKET AND CUTTER ASSEMBLY TO DRIVE THE FIRING PIN AGAINST THE PRIMER AND INITIATE THE EXPLOSIVE TRAIN.

Oct. 26, 1971 Am ETAL 3,615,156

REEFING LINE CUTTER Filed June 6, 1969- 2 Sheets-Sheet l INVENTOR.

G. M. BLAIN ETAL REEFING LINE CUTTER 2 Sheets-Sheet 2 Filed June 6, 19 9 .4 wzawfl 8m INVENTOR.

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United States Patent *Ofice Patented Oct. 26, 1971 US. Cl. 244150 6 Claims ABSTRACT OF THE DISCLOSURE An explosively actuated cutter assembly for severing the reefing lines which hold together the canopy of a parachute as the latter is deployed. The explosive which drives the cutter blade through the reefing line is detonated by utilizing the tension developed in the reefing line by the tendency of the parachute to unfurl to drive a firing pin against a primer. The explosive train within each cutter assembly may be identical; that is, there is no necessity for different delay times to provide sequential severing of the reefing lines to that nearest the parachute canopy apex from the load since the reefing lines are automatically tensioned in that order as the parachute is unfurled. An inexpensive bracket is provided in combination with the movable cutter assembly to hold the reefing line with an initial kink or bend which is straightened by tension in the line, thereby causing relative movement of the bracket and cutter assembly to drive the firing pin against the primer and initiate the explosive train.

The present invention relates to explosively actuated parachute reefing line cutters and, more specifically, to a novel cutter assembly which is actuated without the use of the usual lanyards between the assembly and the load carried by the parachute.

In order to insure that parachutes used in air delivery of relatively heavy cargo loads are properly deployed, it is a common practice to bind the parachute canopy with reefing lines which are sequentially released beginning with the line nearest the load. Among the conventional devices used for severing reefing lines in this manner are those wherein a cutter blade is driven through the reefing line by detonation of an explosive charge. Prior to severin g of the first reefing line the main parachute canopy and shroud lines may be strung out in a line by the use of a smaller drogue parachute. The firing assemblies of the cutters associated with each reefing line are commonly activated by a lanyard extending between the load and the cutter assemblies. As the load falls away from the main canopy a triggering mechanism is tripped by the lanyard to ignite a percussion primer. Using a sequence of delay times in the firing trains of the several cutter assemblies, a gradual opening of the main canopy is provided until the last cutter assembly severs the reefing line nearest the apex and full deployment is achieved.

Present designs are unreliable because the triggering mechanism, commonly provided in the form of a relatively complex sear-spring assembly, tends to jam when the lanyard is pulled at the wrong angle relative to the reefing line cutter. Also, pyrotechnic delays with a variety of long delay times in small packages are generally not very accurate, causing improper sequencing of reefing line cutting, and necessitating additional care and expense in assembly since the cutter assemblies must be placed in the proper sequence with that having the shortest delay time nearest the load and that with the longest delay time nearest the apex. In addition, existing designs are relatively heavy, complex, and sometimes tear the canopy during initial deployment.

A principal object of the present invention is to provide an explosively actuated reefing line cutter which is simple and economical in design, highly reliable in operation, and eliminates the need of a lanyard attached between the cutter assembly and the load to provide actuation.

A further object is to provide a parachute reefing line cutter which is actuated by the tension placed in the reefing line by the natural tendency of the parachute canopy to open.

An additional object is to provide an explosively actuated parachute reefing line cutter which will provide severing of a plurality of reefing lines in proper sequence without the use of different pyrotechnic delay times in the explosive trains of the various cutters.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts, which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a typical cargo parachute and load illustrating the general environment of use of the present invention;

FIG. 2 is a plan view showing the general structure of a preferred embodiment of the invention, with a section of the reefing line to be severed, shown in a first position;

FIG. 3 is a plan view of the mechanism of FIG. 2 shown in a second position;

FIG. 4 is 'a side elevational view in vertical section along the line 4-4 of FIG. 3 showing internal details of a portion of the mechanism; and

FIG. 5 is a fragmentary, sectional view on the line 5-5 of FIG. 4 showing additional details of construction.

FIG. 1 illustrates the general manner of initial deployment of a typical cargo parachute. Upon ejection of the load and parachute from the aircraft, a relatively small drogue chute, indicated generally by the reference numeral 19, is commonly employed to string out the main chute canopy and shroud lines in a line from the load before initial deployment of the main chute. Load 12 is supported by sling or harness 14 which is attached to one end of each of the shroud lines 16, the latter being attached at their opposite ends around the periphery of canopy 18. A plurality of reefing lines 20 are utilized to reef the canopy, that is, to bind the canopy in a bundle at several points between shroud lines 16 and canopy apex. The reefing line nearest shroud lines 16 is released first, thereby allowing the canopy to begin to open. As succeeding reefing lines are released in sequence toward apex, shroud lines 16 may spread further apart toward the ends connected to the canopy, thereby allowing the latter to be gradually fully deployed. The sequential release of the reefing lines to provide gradual opening of the parachute canopy to insure that the latter does not become entangled in the shrouds or otherwise fail to deploy properly.

The cutter assembly of the present invention which severs the reefing lines to provide gradual deployment of the canopy as described above is shown in FIGS. 2 and 3 with a segment of reefing line 20. The assembly is designated generally by the reference numeral 22 and one of such assemblies is associated with each reefing line on the parachute. Cutter assembly 22 may be conveniently fabricated of plastic or other such easily formable, inexpensive material, and comprises elongated housing means 24 having an internal cylindrical cavity 26 wherein firing assembly 28 is slideably inserted and initially retained, as set forth in more detail later, by shear pin 30. A pair of spaced arms 32 and 34 extend from housing means 24 on each side of the end of firing assembly 28 extending out of cavity 26. Each of arms 32 and 34, as Well as firing assembly 28, include openings through which reefing line may be loosely inserted. The various elements are so positioned and arranged that when initially assembled firing assembly 28 is held by shear pin 30 with its opening out of alignment with the openings in arms 32 and 34, thereby providing a substantially pronounced kink or bend in reefing line 20.

After canopy 18 has been released and strung out as shown in FIG. 1, it will tend to open in the usual manner through air resistance. This tends to spread the canopy, thereby producing a high tension force in the reefing line closest to the throud lines. This force, which may be as great as 7,000 lbs., straightens the kink in the reefing line, breaking shear pin 30 and causing firing assembly 28 to slide rapidly to the rear of cavity 26. The parts are so dimensioned, and the initial position in which explosive assembly 28 is retained by shear pin 30 is such that the straightening of reefing line 20 by the tension force therein is suflicient to drive protruding end portion 36 of a firing pin, described later in more detail, sharply against rear surface 38 of cavity 26. Openings 40 may be provided between the interior of cavity 26, near rear surface 38 thereof, and the outside atmosphere in order to expel the air from the interior of cavity 26 as firing assembly 28 moves rearwardly therein.

Turning now to FIGS. 4 and 5, details of firing assembly 28 are shown in more detail. The assembly comprises a cylindrical outer casing 42, open at both ends, having an opening 42 extending laterally therethrough for accommodation of reefing line 20. Firing pin 44 is supported within casing 42 'by sleeve 46 which is retained between lockring 48 and welded metal closure 49. Explosive container 50 positioned with one end adjacent the opposite side of closure 49, holds all explosive mixes and chemicals associated with the device of the invention, and therefore may be conveniently fabricated as a separate subassembly before incorporation in casing 42 during final assembly of the device. Primer 52 is supported adjacent closure 49 to receive therethrough the shock transmitted by firing pin 44 as the latter is driven forwardly by impact of end portion 36 thereof with surface 38 of cavity 26. Primer 52 comprises a standard percussion primer, and succeeding elements in the explosive train are: porous plug or air gap filter 54, ignition mix 56, delay mix 58, transfer change 60, and output charge 62. Many suitable examples of conventional chemical explosives will be readily known to those skilled in the art for use as each of the aforementioned elements in the explosive train. The particular explosives used and, in fact, the design of the explosive train as a whole, are largely matters of choice and subject to wide variation within the scope of the invention.

Knife edge 64 forms a terminal portion of cutter blade piston 66 which extends into the end of explosive holder 50 adjacent the end of the explosive train. The cutter piston is held in its initial position by shear pin 68, extending through the cutter blade piston and into the walls of casing 42. When the explosive train is detonated cutter blade piston 66 is driven forwardly by the force of the explosion to break shear pin 68 and force knife edge 64 of the cutter blade through reefing line 20. The reefing line is held against anvil 70 as it is cut, the anvil being retained between the reefing line and lockring 72. As seen more clearly in FIG. 5, shear pin 30 is anchored at each end in housing means of cutter assembly 22, and extends through casing 42, sleeve 46 and firing pin 44. When tension is applied to reefing line 20 a rearward force is applied to explosive assembly 28, breaking shear pin 30 between housing means 24 and casing 42, thereby allowing the assembly to slide rearwardly in cavity 26 until end portion 36 of firing pin 44 strikes rear wall 38 of cavity 26. The remaining elements of firing assembly 28 continue to travel rear-wardly for a short distance after firing pin 44 is stopped, thereby breaking shear pin 30 again on each side of the firing pin. The impact of raised end portion 74, transmitted through closure 49 t0 primer 52, detonates the primer. The hot gases from the primer penetrate porous plug 54 to ignite ignition mix 56. In turn, the standard delay mix 62 burns for the required delay time (typically 2 seconds) and then sets off transfer charge 60. The output charge then fires, producing gas pressures which cause cutter piston 66 to fracture shear pin 68 and drive cutter blade through the reefing line against anvil 70. O-rings 76 and 78 are provided as indicated in FiG. 4 to prevent excess leakage of the detonation gases for added efiiciency. When the first reefing line is cut, the canopy springs free at that point and spreads apart to transfer the point of stress to the next highest reefing line. The reefing line cutter sequence then occurs again, and so on, until the last reefing line is cut and the parachute is fully deployed.

From the foregoing description it may be seen that the device of the present invention provides many advantages of simplicity, economy and reliability over conventional prior art devices used for the same purpose. For example, the expensive seal-spring triggering mechanism is eliminated, and with it the problem of lanyard pull angle. Also, the lanyard and metal brackets commonly provided to transfer lanyard pull to the triggering mechanism are omitted, thus further simplifying the system. Proper sequencing of reefing line cutting is automatically assured because no reefing line cutter can be actuated until the immediately preceedin'g reefing line has been severed. An additional advantage is that a standard delay time may be used in the explosive train of all cutter devices and short delay times are readily obtainable in reliable designs. The automatic sequencing of the reefing line cutting also permits much wider tolerances in the delay times.

What is claimed is:

1. A device for severing a paracute reefing line comprising:

(a) a first member having an opening through which said reefing line passes and an enclosed chamber;

(b) an explosive charge within said chamber;

(c) cutting means disposed for severing movement through said line in response to detonation of said explosive charge;

(d) a second member having means constraining the path of said line into bends on each side of said first member when said first and second members are in an initial relative position;

(e) means maintaining said first and second members in said initial position and breakable upon application of tension to said reefing line as the parachute tends to open, thereby straightening said bends and moving said first and second members to a terminal relative position; and

(f) a firing pin disposed to be driven into detonating engagement with said explosive charge by movement of said first and second members from said initial to said terminal positions.

2. The invention according to claim 1 wherein said first member carries said firing pin extending from one end thereof and said opening, through which said reefing line passes, is substantially adjacent the other end.

3. The invention according to claim 2 wherein said first member is elongated along an axis, said firing pin being movable substantially along said axis and said opening extending through said first member transversely to said axis.

4. The invention according to claim 1 wherein said second member includes a central portion supporting said 5 6 first member and said constraining means comprise a pair References Cited of spaced portions, one on each side of said first member. UNITED STATES PATENTS 5. The invention according to claim 4 wherein said means maintaining said first and second members in said 2,942,818 6/1960 Stott 244-150 initial position comprise at least one shear pin extending 5 3,047,261 7/1962 Bockelmann 244150 lsaggvlegnnsgindbigst member and said central portion of said FOREIGN PATENTS 6. The invention according to claim 5 wherein said 818,873 10/1937 France. central portion includes a cavity in which said one end of said first member is supported, said firing pin moving 10 MILTON BUCHLER, pflmary Examlnel' into engagement with the end wall of said cavity when C. RUTLEDGE, Assistant Examiner said members are moved to said terminal position. 

